Intervertebral Implant for Transforminal Posterior Lumbar Interbody Fusion Procedure

ABSTRACT

An intervertebral implant for fusing vertebrae is disclosed. The implant may have a body with curved, posterior and anterior faces separated by two narrow implant ends, superior and inferior faces having a plurality of undulating surfaces for contacting vertebral endplates, and at least one depression in the anterior or posterior face for engagement by an insertion tool. The implant may also have one or more vertical through-channels extending through the implant from the superior face to the inferior face, a chamfer on the superior and inferior surfaces at one of the narrow implant ends, and/or a beveled edge along a perimeter of the superior and inferior faces. The implant configuration facilitates transforaminal insertion of the implant into a symmetric position about the midline of the spine so that a single implant provides balanced support to the spinal column. The implant may be formed of a plurality of interconnecting bodies assembled to form a single unit. An implantation kit and method are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/301,759, filed Dec. 12, 2005, which is a continuation of U.S. patentapplication Ser. No. 10/293,997, filed Nov. 13, 2002, now U.S. Pat. No.6,974,480, which is a continuation-in-part of U.S. patent applicationSer. No. 09/848,178, filed May 3, 2001, now U.S. Pat. No. 6,719,794.

FIELD OF THE INVENTION

The present invention is directed to an intervertebral implant, itsaccompanying instrumentation and their method of use. More particularly,the present invention is directed to an intervertebral implant andinstrumentation for use in a transforaminal posterior lumbar interbodyfusion procedure.

BACKGROUND OF THE INVENTION

A number of medical conditions such as compression of spinal cord nerveroots, degenerative disc disease, herniated nucleus pulposus, spinalstenosis and spondylolisthesis can cause severe low back pain.Intervertebral fusion is a surgical method of alleviating low back pain.In posterior lumbar interbody fusion (“PLIF”), two adjacent vertebralbodies are fused together by removing the affected disc and insertingposteriorly one or more implants that would allow for bone to growbetween the two vertebral bodies to bridge the gap left by the removeddisc.

One variation of the traditional PLIF technique is the transforaminalposterior lumbar interbody fusion (T-PLIF) technique. Pursuant to thisprocedure, an implant is inserted into the affected disc space via aunilateral (or sometimes bilateral), posterior approach, offset from themidline of the spine, by removing portions of the facet joint of thevertebrae. The T-PLIF approach avoids damage to nerve structures such asthe dura, cauda equina and the nerve root, but the resultingtransforaminal window available to remove the affected disc, prepare thevertebral endplates, and insert the implant is limited laterally by softtissue and medially by the cauda equina.

A number of different implants typically used for the traditional PLIFprocedure have been used for the T-PLIF procedure with varying success.These include threaded titanium or polymer cages, allograft wedges,rings, etc. However, as these devices were not designed specifically forthe T-PLIF procedure, they are not shaped to be easily insertable intothe affected disc space through the narrow transforaminal window, andmay require additional retraction of the cauda equina and nerve roots.Such retraction can cause temporary or permanent nerve damage. Inaddition, some of these implants, such as the threaded titanium orpolymer cage, suffer from the disadvantage of requiring drilling andtapping of the vertebral endplates for insertion. Further, the incidenceof subsidence in long term use is not known for such cages. Finally,restoration of lordosis, i.e., the natural curvature of the lumbar spineis very difficult when a cylindrical or square titanium or polymer cageis used.

As the discussion above illustrates, there is a need for an improvedimplant and instrumentation for fusing vertebrae via the transforaminallumbar interbody fusion procedure.

SUMMARY OF THE INVENTION

The present invention relates to an intervertebral implant (“T-PLIFimplant”) and its use during a transforaminal lumbar interbody fusionprocedure. In a preferred embodiment, the T-PLIF implant has an arcuatebody with curved, preferably substantially parallel, posterior andanterior faces separated by two narrow implant ends, and superior andinferior faces having textured surfaces for contacting upper and lowervertebral endplates. Preferably, the textured surfaces compriseundulating structures which may include projections, such as teeth, of asaw-tooth or pyramidal configuration, or ridges which preferablypenetrate the vertebral endplates and prevent slippage. The narrowimplant ends may be rounded or substantially flat. The arcuate implantconfiguration facilitates insertion of the implant via a transforaminalwindow. The implant, which may be formed of allogenic bone, metal, orplastic, may also have at least one depression, such as a channel orgroove, in the posterior or anterior face for engagement by an insertiontool, such as an implant holder. In a preferred aspect, the superior andinferior faces are convex, and the thickness of the implant tapers withits greatest thickness in the middle region between the narrow ends ofthe implant, i.e., at a section parallel to a sagittal plane, anddecreasing toward each of the narrow ends.

In another embodiment, the T-PLIF implant preferably has curved,substantially parallel posterior and anterior faces extending along alongitudinal axis of the implant, a pair of convex narrow endsseparating the posterior and anterior faces, a chamfer on the superiorand inferior faces at one of the convex narrow ends, a beveled edgealong a perimeter of the superior and inferior faces, and at least onedepression in the anterior or posterior face for engagement by aninsertion tool, where the superior and inferior faces contact upper andlower vertebral endplates and define a thickness of the implant. TheT-PLIF implant preferably has at least two vertical through-channelsextending through the implant from the superior face to the inferiorface, each vertical through-channel having a width and walls onposterior and anterior sides of the width. The arcuate implantconfiguration and the chamfer on the inferior and superior faces at thenarrow insertion end of the implant facilitate insertion of the implantvia the transforaminal window. In a preferred aspect, the implant alsohas at least two anterior-posterior horizontal through-channelsextending through the implant from the posterior face to the anteriorface. The implant may also feature at least one lateral horizontalthrough-channel extending from a narrow end of the implant inward towardan adjacent anterior-posterior horizontal through-channel. Each of thechannels may be packed with bone-graft and/or bone growth inducingmaterial to aid in spinal fusion. In one exemplary embodiment, the wallson the posterior and anterior sides of the width of the verticalthrough-channels have a thickness greater than the width of the verticalthrough channels. The implant may be formed of a radiolucent polymermaterial selected from the polyaryl ether ketone family (PAEK), such aspolyether ether ketone (PEEK) or polyether ketone (PEKK), or othersuitable biocompatible material of sufficient strength, such astitanium. The implant may include one or more radiopaque marker, such aspins or screws, extending substantially through the thickness of theimplant to indicate implant location and size in postoperative spinalscans.

In another preferred embodiment, the implant is formed of a plurality ofinterconnecting bodies assembled to form a single unit. In thisconfiguration, the plurality of interconnecting bodies forming theT-PLIF implant may be press-fit together and may include one or morepin(s) or screw(s) extending through an opening in the plurality ofbodies to hold the bodies together as a single unit. Adjacent surfacesof the plurality of bodies may also have mating interlocking surfacesthat aid in holding the bodies together as a single unit.

In still another preferred embodiment, the present invention relates toa kit for implanting an intervertebral implant into an affected discspace of a patient via a transforaminal window. The kit includes animplant having an arcuate body with curved, preferably substantiallyparallel, posterior and anterior faces separated by two narrower implantends, superior and inferior faces preferably having a textured surface,such as projections or teeth, for contacting and preferably penetratingupper and lower vertebral endplates. The superior and inferior faces maydefine a thickness. Preferably the implant has at least one depressionin its posterior or anterior face near one of its ends for engagement byan insertion tool. The implant may also have two or more verticalthrough-channels extending through the implant from the superior face tothe inferior face, each vertical through-channel having a width andwalls on posterior and anterior sides of the width, a chamfer on thesuperior and inferior surfaces at an insertion end and a beveled edgealong a perimeter of the superior and inferior faces. The kit mayfurther include one or more trial-fit spacer(s) for determining theappropriate size of the implant needed to fill the affected disc space,an insertion tool having an angled or curved neck for holding andproperly positioning the implant during insertion through thetransforaminal window, and an impactor having an angled or curved neckfor properly positioning the implant within the affected disc space. Theface of the impactor may be concavely shaped to mate with the narrow endof the T-PLIF implant during impaction. The kit may further include alamina spreader for distracting vertebrae adjacent to the affected discspace, an osteotome for removing facets of the vertebrae adjacent to theaffected disc space to create a transforaminal window, one or morecurettes, angled and/or straight, for removing disc material from theaffected disc space, a bone rasp for preparing endplates of thevertebrae adjacent the affected disc space, and a graft implant tool forimplanting bone graft material into the affected disc space. The kit maystill further include a curved guide tool to guide the implant into theaffected disc space. In another preferred embodiment, the implant of thekit includes two or more anterior-posterior horizontal through-channelsextending through the implant from the posterior face to the anteriorface, wherein a portion of the walls on the posterior and anterior sidesof the width of the vertical through-channels of the implant may have athickness greater than the width of the vertical through channels. Theimplant of the kit may also include one or more lateral horizontalthrough-channel(s) extending from a narrow end of the implant inwardtoward an adjacent anterior-posterior horizontal through-channel. Eachof the channels may be packed with bone-graft and/or bone growthinducing material prior to and/or after insertion to aid in spinalfusion. The implant may also include one or more radiopaque markers,such as pins, that extend substantially through the thickness of theimplant.

In yet another aspect, a method for implanting an intervertebral implantinto an affected disc space of a patient via a transforaminal window isdescribed. The transforaminal window is created, the disc space isprepared and bone graft material may be inserted into the affected discspace. Using an insertion tool, an implant is inserted into the affecteddisc space via the transforaminal window and seated in a portion of thedisc space closer to the anterior edge of the disc space than theposterior edge of the disc space. As discussed above, the implantpreferably has an arcuate body with curved, substantially parallelposterior and anterior faces separated by two narrow implant ends,superior and inferior faces having a plurality of undulating surfacesfor contacting upper and lower vertebral endplates, and preferably atleast one depression at a first end for engagement by the insertiontool. In the present method, the arcuate implant configurationfacilitates insertion of the implant via the transforaminal window. Theimplant may be inserted along an arcuate path. The method may furthercomprise impacting the implant with an impactor tool to properlyposition the implant within the affected disc space. Either or both theinsertion tool and the impactor tool may be angled to facilitateinsertion, alignment, placement and/or proper seating of the implant.The implant may also feature two or more vertical through-channel(s)extending through the implant from the superior face to the inferiorface, each vertical through-channel having a width and walls onposterior and anterior sides of the width, a chamfer on the superior andinferior faces at the insertion end, and a beveled edge along aperimeter of the superior and inferior faces. The implant may also havetwo or more anterior-posterior horizontal through-channel(s) extendingthrough the implant from the posterior face to the anterior face and/orat least one lateral horizontal through-channel extending from a narrowend of the implant inward toward an adjacent anterior-posteriorhorizontal through-channel. Each of the channels may be packed withbone-graft and/or bone growth inducing material before implantationand/or after implantation to aid in spinal fusion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a typical human vertebrae showing thetransforaminal window through which an implant according to the presentinvention is inserted;

FIG. 2A is a cross-section view of an embodiment of an implant accordingto the present invention;

FIG. 2B is a side view along the longer axis of the implant of FIG. 2A;

FIG. 2C is a cross-section view taken along line 2C-2C of FIG. 2B;

FIG. 2D is a perspective view of the implant of FIG. 2A;

FIG. 3A is a partial cross-section view of another embodiment of animplant according to the present invention;

FIG. 3B is a partial cross-section view along the longer axis of theimplant of FIG. 3A;

FIG. 3C is a cross-section view taken along line 3C-3C of FIG. 3B;

FIG. 3D is a perspective view of the implant of FIG. 3A;

FIG. 4 is a perspective view of still another embodiment of the implantof the present invention;

FIG. 5 is an axial view of a typical human vertebrae showing the implantof FIG. 4 in an asymmetric final position.

FIG. 6 is a posterior view of a section of human spine prior topreparation of the transforaminal window;

FIG. 7 is a posterior view of a section of human spine with thetransforaminal window prepared;

FIG. 8A depicts an angled bone curette for use during the T-PLIFprocedure;

FIG. 8B depicts another angled bone curette for use during the T-PLIFprocedure;

FIG. 8C depicts an angled bone curette removing disc material from anaffected disc space;

FIG. 9A depicts an angled bone rasp for use during a T-PLIF procedure;

FIG. 9B depicts an angled bone rasp removing material from an affecteddisc space;

FIG. 10A depicts a trial-fit spacer for use during a T-PLIF procedure;

FIG. 10B depicts a trial-fit spacer being inserted into an affected discspace via a transforaminal window;

FIG. 11A depicts an implant holder for use during a T-PLIF procedure;

FIG. 11B depicts the tips of the implant holder shown in FIG. 11A;

FIG. 11C depicts an posterior view of the human spine showing a T-PLIFimplant being inserted with an implant holder;

FIG. 11D depicts a top view of a human vertebrae showing a T-PLIFimplant being inserted with in an implant holder;

FIG. 12 depicts an implant guide tool for use with the T-PLIF implant;

FIG. 13A depicts an angled impactor tool for use with the T-PLIFimplant;

FIG. 13B is a close-up view of the tip of the impactor tool shown inFIG. 13A;

FIG. 14 is a top view of a typical human vertebrae showing an implantaccording to the present invention being properly positioned into anaffected disc space using the impactor tool shown in FIG. 13A;

FIG. 15 is a top view of the vertebrae of FIG. 1 showing the T-PLIFimplant in a final position; and

FIG. 16A is a partial cross-section side view along the longer axis ofstill another embodiment of an implant according to the presentinvention;

FIG. 16B is a partial cross-section side view along the shorter axis ofthe implant of FIG. 16A;

FIG. 16C is a partial cross-section top view of the implant of FIG. 16A;

FIG. 16D is a perspective view of the implant in FIG. 16A;

FIG. 16E is a partial side view of the implant taken along line 16E-16Ein FIG. 16C;

FIG. 17A is a partial cross-section side view along the longer axis ofstill another embodiment of an implant according to the presentinvention;

FIG. 17B is a partial cross-section side view along the shorter axis ofthe implant of FIG. 17A;

FIG. 17C is a partial cross-section top view of the implant of FIG. 17A;and

FIG. 17D is a perspective view of the implant in FIG. 17A;

FIG. 17E is a partial side view of the implant taken along line 17E-17Ein FIG. 17C; and

FIG. 18 is a side view of another preferred embodiment of the implant ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

While various descriptions of the present invention are provided below,it should be understood that these descriptions are intended toillustrate the principals of the present invention and its variousfeatures, which can be used singly or in any combination thereof.Therefore, this invention is not to be limited to only the specificallypreferred embodiments described and depicted herein.

The transforaminal posterior lumbar interbody fusion implant (“T-PLIFimplant”) is designed for use as an intervertebral spacer in spinalfusion surgery where an affected disk is removed from between twoadjacent vertebrae and replaced with an implant that provides segmentalstability and allows for bone to grow between the two vertebrae tobridge the gap created by disk removal. Specifically, the T-PLIF implantis designed for the transforaminal lumbar interbody fusion (T-PLIF)technique, which, as shown in FIG. 1, involves a posterior approach 12,offset from the midline 14 of the spine, to the affected intervertebraldisk space 16. The window 18 available for implant insertion using theT-PLIF technique is limited medially by the dura or cauda equina 20 andthe superior exiting nerve root (not shown).

As shown in FIGS. 2A through 2D, in a preferred embodiment, the T-PLIFimplant has an arcuate, “rocker-like” body 22 with curved anterior andposterior faces 24, 26 to facilitate the offset insertion of the implantthrough the narrow approach window 18 into the disk space. Preferably,the anterior and posterior faces 24 and 26 are substantially parallel,separated by a pair of narrow ends 25. Narrow ends 25 may be rounded orblunt. The superior and inferior surfaces 28, 30 preferably haveprojections, such as teeth 32, for engaging the adjacent vertebrae.Teeth 32 on superior and inferior surfaces 28, 30 preferably provide amechanical interlock between implant 22 and the end plates bypenetrating the end plates. The initial mechanical stability afforded byteeth 32 minimizes the risk of post-operative expulsion/slippage ofimplant 22. Teeth 32 may have a saw-tooth shape, where one side of thetooth is perpendicular to the superior or inferior surface, or a pyramidshape, where each tooth has four sides and forms an acute angle with thesuperior or inferior face. Preferably, implant body 22 has at least onechannel or slot 34 on one end of implant 22 for engagement by a surgicalinstrument, such as an implant holder 66 (shown in FIG. 11A). It shouldbe noted that implant 22 may also be configured with a channel 34 ononly one side or without channels altogether. Other known methods forengaging the implant with surgical instruments, such as a threaded borefor receiving the threaded end of a surgical tool or a non-threaded borefor receiving an expandable head of an insertion tool, may also be used.

As shown in FIG. 2B, thickness 31 of implant 22 is greatest at themid-section between the two narrow implant ends 25 and tapers graduallyalong the longitudinal axis 36 of implant 22 so that it is thinnest atthe narrow ends 25 of implant 22. The taper is preferably arcuate andprovides a convex configuration and a proper anatomical fit, while alsofacilitating insertion of implant 22 into the affected disc space. Itshould be noted that in a preferred embodiment, thickness 31 does nottaper or change along the shorter axis 37 of implant 22. Thus for anygiven cross section taken perpendicular to the longitudinal axis 36 ofthe implant, the distance between the superior and inferior surfaces 28and 30 remains substantially constant. In alternate embodiments,however, thickness 31 may change or taper along shorter axis 37 ofimplant 22. The dimensions of implant 22 can be varied to accommodate apatient's anatomy, and the thickness of the implant is chosen based onthe size of the disk space to be filled. Preferably, implant 22 has amaximum thickness 31 at its mid-section of about 7.0 to about 17.0 mm,and may be formed of metal, allograft, a metal-allograft composite, acarbon-fiber polymer, pure polymer or plastic or combinations of thesematerials. The implant may also be formed of a resorbable polymer. Thethickness at the narrow ends 25 of implant 22 may range from about 1.5to about 2.0 mm less than the maximum thickness at the mid-section. Theimplant may range from about 26 to about 32 mm in length, and have awidth from about 9 to 11 mm. Implant 22, which as shown most clearly inFIG. 2A is symmetric about at least one axis of rotation 37, is intendedfor symmetric placement about the midline 14 of the spine (see FIG. 19).The arcuate configuration of implant 22 facilitates insertion of theimplant from the transforaminal approach into a symmetric position aboutthe midline of the spine so that a single implant provides balancedsupport to the spinal column.

As shown in FIGS. 3A-3D, in an alternate embodiment implant 22 may beformed of two or more pieces 38 preferably having interlocking grooves39 and pallets 40 that may be press-fit and fastened together with pinsor screws 42. The number and orientation of pins or screws 42 can bevaried. In addition or alternatively, the pieces may be fastened usingglue, cement or a welding or bonding process. This multi-componentconfiguration may be particularly useful for implants formed ofallograft bone, since it may be difficult and/or impractical to obtain asingle, sufficiently large piece of allograft for some applications. Inthe case of implants formed completely of artificial (i.e.,non-allograft) materials, such as steel, plastic or metallic ornon-metallic polymer, a one-piece implant may be more practical. Asshown in FIG. 3C, in a preferred embodiment for any given cross-sectiontaken perpendicular to the longitudinal axis of the implant, thedistance between the superior and inferior surfaces 28 and 30 remainssubstantially constant.

As in the previous embodiment, the anterior and posterior faces 24, 26are preferably substantially parallel, and, as shown, may be defined byradii of curvature R1 and R2, where R1, for example, may be in the rangeof 25-35 mm and preferably about 28 mm and R2, for example, may be inthe range of 15 to 25 mm and preferably about 19 mm. The superior andinferior surfaces 28, 30 are arcuate shaped and the implant has athickness 31, which is preferably greatest at a center portion betweennarrow ends 25 and gradually tapers becoming thinnest at narrow ends 25.Tapering thickness 31 may be defined by a radius of curvature R3, whereR3 for example, may be in the range of 85 to 115 mm and preferably about100 mm. As shown, the component pieces 46, 48 of implant 22 have holes44 to accommodate pins or screws 42. Holes 44 are preferably drilledafter component pieces 38 have been stacked one on top of the other. Themultiple pieces 38 are then assembled with screws or pins 42 so thatpractitioners receive the implant 22 as a single, pre-fabricated unit.The upper component piece 46 has an arcuate superior surface preferablywith teeth 32, while its bottom surface is preferably configured withgrooves and pallets preferably to interlock with the upper surface oflower component piece 48. The arcuate inferior surface 30 of lowercomponent piece 48 also preferably has teeth 32 for engaging the lowervertebral endplate of the affected disc space. Either or both superiorand inferior surfaces 28, 30 may have ridges, texturing or some otherform of engaging projection in place of teeth 32.

Reference is now made to FIGS. 16A-16E, which display still anotherpreferred embodiment of the implant of the present invention. Similar inprofile to the embodiments shown in FIGS. 2A and 3A, the anterior andposterior faces 24, 26 are substantially parallel, and, as shown, may bedefined by radii of curvature R1 and R2, where R1, for example, may bein the range of 25 to 35 mm and preferably about 29 mm and R2, forexample, may be in the range of 15 to 25 mm and preferably about 19 mm.The superior and inferior surfaces 28, 30 are arcuate shaped and theimplant has a thickness 31, which is preferably greatest at a centerportion between narrow ends 25 and gradually tapers becoming thinnest atnarrow ends 25. Tapering thickness 31 may be defined by a radius ofcurvature R3, where R3 for example, may be in the range of 85 to 115 mmand preferably about 100 mm. Superior and inferior surfaces 28, 30preferably have a textured surface which may include a plurality ofundulating surfaces, such as, for example, teeth 32, for engaging theupper and lower vertebral endplates of the affected disc space. (Note:For sake of clarity, teeth 32 are not pictured in FIGS. 16C-16E, 17C-17Eor on the inferior face of the implant shown in FIGS. 16B & 17B.)

As shown, the implant has depressions or slots 34 on both its anteriorand posterior face that mate with an insertion tool 66 (shown in FIGS.11A & 11B). As shown in FIGS. 11B, 16C and 17C, projections 69 on thetips 67 of insertion tool 66 mate with scalloped depressions 81 withinslots 34 to securely hold the implant during insertion. The implant hasa pair of vertical through-channels 74 extending through the implantfrom the superior surface 28 to the inferior surface 30, which may bepacked with bone graft and other bone growth inducing material prior toand/or after implantation to aid in spinal fusion. Preferably, theimplant also has a chamfer 75 on both its superior and inferior surfaces28, 30 at insertion end 79. As shown best in FIGS. 16D and 16E, chamfers75 form a wedge-like shape at insertion end 79 to facilitate implantinsertion through the transforaminal window. Chamfers 75 begin at asection of the implant at an angle β from the midline of the implant,where β may be in the range of 15° to 30° and preferably about 23°, andtaper to the end of narrow insertion end 79. As shown in FIG. 16E,chamfers 75 form an angle γ with the vertical wall of narrow insertionend 79, where γ may be in the range of 50° to 80° and preferably about60°.

Preferably, implant 22 also includes a beveled edge 76 along theperimeter of its superior and inferior surfaces 28, 30 As shown in FIG.16B, beveled edge 76 may be beveled at an angle α to the vertical axis,which may be in the range of 25° to 45° and preferably about 37°.Beveled edge 76 is free from teeth 32 and both facilitates implantinsertion and handling of the implant by physicians. Since edges 76 arefree from teeth 32, the perimeter edges of the implant are unlikely tobecome snagged by tissue during implant insertion and a surgeon is lesslikely to tear protective gloves while handling the implant prior to andduring insertion.

As shown in FIG. 16C, in a preferred embodiment, the thickness of thewalls T1 on the anterior and posterior sides of verticalthrough-channels 74 is greater than the width W1 of verticalthrough-channel 74. For example, for an implant with walls of equalthickness, T1 may be in the range of 3.4 to 4.0 mm and preferably about3.5 mm and W1 may be on the order of 3.2 to 2.0 mm. The total implantwidth may be in the range of 9 to 11 mm, and preferably about 10 mm. Itshould be emphasized that the implant shown in FIGS. 16A-16C has walls82 of equal thickness T1 on either side of channel 74, but in otherembodiments walls 82 may have different thicknesses. Channels 74 mayhave an arcuate shape or any other suitable shape, e.g., rectangular,circular, etc. The implant may be formed of a radiolucent materialselected from the polyaryl ether ketone family (PAEK), such as polyetherether ketone (PEEK) or polyether ketone (PEKK), and may includeradiopaque markers, such as pins 77, that act as radiographic markers toaid in positioning and monitoring the position of the implant.Preferably, radiopaque pins 77 extend substantially through the heightof the implant so that postoperative spinal scans indicate the size ofthe implant used in a given patient. For example, a radiolucent implantwith a 7.0 mm height includes radiopaque pins on the order of 6.0 mm inlength, while a 17.0 mm implant has pins on the order of 16.0 mm inlength. Pins 77 thus enable a physician to better evaluate apostoperative patient and monitor the position of the implant. Pins 77may also function as fasteners for implants formed of two or morepieces. The implant may also be formed of a suitable biocompatiblematerial such as titanium. As shown in FIG. 18, the implant may beformed of a stack of units to create an implant with a varying heightsH1 ranging from about 7.0 mm to about 88.0 mm.

In still another embodiment shown in FIGS. 17A-17E, in addition tovertical through-channels 74, the implant has two horizontalthrough-channels 78 extending through the implant from anterior face 24to posterior face 26. Channels 78 may have a width W2 in the range of2.5 to 7.5 mm and preferably about 5.0 mm, and a radius of curvature R4in the range of 1.0 to 2.0 mm and preferably about 1.2 mm. The implantmay also have at least one lateral horizontal through-channel 80extending from a narrow end 25 toward an adjacent anterior-posteriorhorizontal through-channel 78. Lateral through channel 80 may have awidth W3 in the range of 2.0 to 5.0 mm and preferably about 3.0 mm, anda radius of curvature R5 in the range of 1.0 to 2.0 mm and preferablyabout 1.2 mm. Preferably, the implant has lateral horizontalthrough-channels 80 at both narrow ends 25. Alternatively, a singlelateral horizontal through channel may extend from one narrow end 25completely through the implant to the other narrow end 25. Wall 84between horizontal through-channels 78 may have a thickness in the rangeof 2.0 to 4.0 mm and preferably about 2.2 mm. Channels 78, 80 may berectangular, trapezoidal or circular in shape, and may be packed withbone graft or other bone growth inducing material before and afterimplant insertion to aid in spinal fusion.

Reference is now made to FIG. 4 which is a perspective view of anotherembodiment an implant. As in the previous embodiment, implant 23 has acurved body with substantially parallel arcuate anterior and posteriorfaces 24, 26, convex superior and inferior surfaces 28, 30 contributingto a tapering thickness 31, and channels 34 for engaging a surgicalinstrument, such as an insertion tool. In this embodiment, implant 23has a substantially straight or blunted narrow end 50 and a curvednarrow end 52 separating parallel, arcuate anterior and posterior faces24, 26. As shown in FIG. 5, the final position of implant 23 in discspace 16 may be asymmetric with respect to midline 14 of the patient'sspine. The final position of implant 22 may also be asymmetric withrespect to the midline of the spine.

As shown in FIGS. 2A, 3A, 16C, 17C and FIG. 11D, the rocker-like shapeof implant 22 enables the surgeon to insert the implant through thenarrow transforaminal window, typically on the range of about 9.0 to15.0 mm wide, and seat the implant in the disc space anteriorly of thedura without disturbing the anterior curtain of the disc space. Thetypical surgical technique for the T-PLIF procedure begins with thepatient being placed in a prone position on a lumbar frame. Prior toincision, radiographic equipment can assist in locating the preciseintraoperative position of the T-PLIF implant. Following incision, thefacets, lamina and other anatomical landmarks are identified. Theaffected vertebrae are distracted using a lamina spreader or a lateraldistractor, both of which are commonly known in the art. In the lattercase, screws may be inserted through the pedicles into the vertebrae tointerface with the lateral distractor. As shown in FIGS. 6 & 7,following distraction, the transforaminal window 54 is created byremoving the inferior facet 56 of the cranial vertebrae and the superiorfacet 58 of the caudal vertebrae using one or more osteotomes 59 and/orautomatic burrs (not shown) of different sizes. A discectomy isperformed during which disc material from the affected disc space may beremoved using a combination of straight and angled curettes. Angledcurettes, which may be configured with rounded profile 60 (FIG. 8A) or arectangular profile 61 (FIG. 8B), enable removal of material on the farside 63 of the disc space opposite transforaminal window 54, as shown inFIG. 8C.

After the discectomy is complete, the superficial layers of the entirecartilaginous endplates are removed with a combination of straight andangled bone rasps. As shown in FIGS. 9A and 9B, angled rasps 62 may beangled to reach far side 63 of the disc space opposite transforaminalwindow 54. Rasps 62 expose bleeding bone, but care should be taken toavoid excess removal of subchondral bone, as this may weaken theanterior column. Entire removal of the endplate may result in subsidenceand loss of segmental stability. Next, an appropriately sized trial-fitT-PLIF spacer/template 64, shown in FIGS. 10A and 10B, may be insertedinto the intervertebral disc space using gentle impaction to determinethe appropriate implant thickness for the disc space to be filled.Fluoroscopy can assist in confirming the fit of the trial spacer. If thetrial spacer 64 appears too loose/too tight, the next larger/smallersize trial spacer should be used until the most secure fit is achieved.For example, if a trial fit spacer with a maximum thickness of 11 mm istoo loose when inserted into the disc space, a physician should try the13 mm thick spacer, and so on. Trial fit spacers preferably range inheight from about 7 mm to about 17 mm.

Upon identifying and removing the best fitting trial spacer, a T-PLIFimplant of appropriate size is selected. At this time, prior toplacement of the T-PLIF implant, bone graft material, such as autogenouscancellous bone or a bone substitute, may be placed in the anterior andlateral aspect of the affected disc space. Channels in implant 22 mayalso be packed with bone graft material prior to insertion. As shown inFIGS. 11C and 11D, T-PLIF implant 22 is then held securely using asurgical instrument such as implant holder 66 (shown more clearly inFIG. 11A), which engages the channels or slots 34 at one end of implant22. The tips 67 of implant holder 66 may be curved or angled to matewith curved implant 22 and facilitate insertion of implant 22 into discspace 16. T-PLIF implant 22 is then introduced into the intervertebraldisc space 16 via the transforaminal window, as shown in FIG. 11C. Aguide tool having a curved blade 68 (shown in FIG. 12) to match thecurvature of the anterior face of implant 22 may be used to properlyguide the implant into affected disc space 16. The implant may be guidedalong an arcuate path to its final position. Slight impaction may benecessary using implant holder 66 (shown in FIG. 11A) or an impactortool 70 (shown in FIG. 13A) to fully seat the implant. As shown in FIGS.13A & 13B, impactor tool 70 may also be curved or angled to facilitateseating of the implant through the narrow transforaminal window. Also,the face 71 of impactor 70 may be concavely shaped to mate with the endof implant 22, as shown in FIG. 14.

Once the T-PLIF implant is in the desired final position, such as thesymmetric final position shown in FIG. 15 or the asymmetric positionshown in FIG. 5, implant holder 66, and possibly guide tool 68, isremoved and additional bone graft material 73 may be inserted into thedisc space and/or the channels 74, 78 and 80 of the implant. Preferably,T-PLIF implant 22 is slightly recessed from the anterior edge 72 of thevertebral body, but implanted in the anterior-most third of the discspace such that the implant is closer to the anterior edge 72 of thedisc space than the posterior edge. As shown in FIG. 15, the curvatureof anterior face 24 of implant 22 is substantially the same as thecurvature of anterior edge 72 of disc space 16. In the symmetric seatedposition shown in FIG. 15, a single T-PLIF implant 22 provides balancedsupport to the spinal column about the midline of the spine.

While certain preferred embodiments of the implant have been describedand explained, it will be appreciated that numerous modifications andother embodiments may be devised by those skilled in the art. Therefore,it will be understood that the appended claims are intended to cover allsuch modifications and embodiments which come within the spirit andscope of the present invention.

1. An intervertebral implant sized and configured for implantationbetween a first and second vertebra via transforaminal lumbar interbodyfusion technique, the implant comprising: a body substantially made ofallograft, the body including a curved posterior face, a curved anteriorface, both curved posterior and anterior faces extending along alongitudinal axis of the implant; a pair of narrow ends separating theposterior and anterior faces and superior and inferior surfaces forcontacting at least a portion of the first and second vertebral, thesuperior and inferior surfaces include a plurality of teeth formed; andat least one non-threaded, horizontal channel configured and adapted forengagement by an implant insertion tool, the channel disposed along atleast a portion of the curved posterior face or disposed along at leasta portion of the curved anterior face.
 2. The implant of claim 1,further comprising at least one vertical through-channel extending fromsaid superior surface to said inferior surface.
 3. The implant of claim1, wherein at least one of the superior and inferior surfaces includes achamfer formed thereon.
 4. The implant of claim 3, wherein the chamferis devoid of any teeth formed thereon.
 5. The implant of claim 3,wherein the implant includes a pair of non-threaded, horizontalchannels, one of said non-threaded, horizontal channel being formed onthe curved posterior face, the other of said non-threaded, horizontalchannel being formed on the curved anterior face, the pair ofnon-threaded, horizontal channels extending from one of the arcuateends.
 6. The implant of claim 5, wherein the chamfer is formed on theother of said arcuate ends.
 7. The implant of claim 1, wherein thecurved anterior and curved posterior faces are substantially parallel.8. The implant of claim 6, wherein the curved posterior face has a radiiof curvature R1 and the curved anterior face has a radii of curvatureR2, wherein R1 is between about 25 mm and 35 mm and R2 is between about15 mm and 25 mm.
 9. The implant of claim 1, wherein the teeth have apyramid shape such that each tooth has four sides and forms an acuteangle with the superior or inferior faces.
 10. The implant of claim 1,wherein a distance between the superior and inferior surfaces define animplant height, the implant height being greatest at a midsectionbetween the pair of narrow ends, the implant height tapering graduallyalong the longitudinal axis of the implant so that the implant height isthinnest at the narrow ends of the implant.
 11. The implant of claim 10,wherein the tapering thickness is defined by a radius of curvature R3,wherein R3 is between about 85 mm and 115 mm.
 12. The implant of claim10, wherein the implant height is substantially constant for any givencross section taken perpendicular to the longitudinal axis of theimplant
 13. The implant of claim 1, wherein the implant is formed of atleast two pieces of allograft assembled together to form the implant.14. The implant of claim 13, wherein the at least two pieces ofallograft are joined together by interlocking grooves and pallets. 15.The implant of claim 13, wherein the at least two pieces of allograftcontaining an opening formed therein, the opening being sized andconfigured to receive at least one pin for holding the pieces ofallograft together as a single unit.
 16. An intervertebral implant sizedand configured for implantation between a first and second vertebra viatransforaminal lumbar interbody fusion technique, the implantcomprising: a body having a curved posterior face, a curved anteriorface, a pair of curved ends separating the posterior and anterior facesand superior and inferior faces for contacting at least a portion of thefirst and second vertebra, the superior and inferior faces defining athickness of the implant; wherein the body includes at least onevertical through-channel extending from the superior face to theinferior face; and the anterior and posterior faces include at least twonon-threaded, horizontal channels configured and adapted for engagementby an implant insertion tool, one of the channels being disposed alongat least a portion of the curved posterior face, the other of saidchannels being disposed along at least a portion of the curved anteriorface, wherein the channels each include at least two recesses forengaging a corresponding projection formed on the insertion tool. 17.The implant of claim 16, wherein the at least one verticalthrough-channel defines a first wall between the anterior face and thevertical through-channel and a second wall between the posterior faceand the vertical through channel, the first and second walls having awall width, the vertical through channel having a channel width, thewall width being greater than the channel width.
 18. The implant ofclaim 16, wherein the implant includes at least two verticalthrough-channels extending from said superior surface to said anteriorsurface.
 19. The implant of claim 16, wherein the implant furtherincludes at least one horizontal through-channel extending through theimplant from the anterior face to the posterior face.
 20. The implant ofclaim 16, wherein the implant further includes at least one lateralthrough-channel extending from at least one of the curved ends towardsthe vertical through channel.
 21. The implant of claim 20, wherein thelateral through channel extends from one curved end completely throughthe implant to the other curved end.
 22. The implant of claim 16,wherein the implant is formed from a radiolucent material.
 23. Theimplant of claim 20, wherein the implant includes at least oneradiopaque marker
 24. The implant of claim 16, wherein the implant isformed from a titanium alloy.
 25. The implant of claim 16 wherein atleast one of the superior and inferior surfaces includes a chamferformed thereon.
 26. The implant of claim 25, wherein the chamfer isdevoid of any teeth formed thereon.
 27. The implant of claim 16, whereinthe implant further includes a beveled edge along a perimeter of thesuperior and inferior surfaces.
 28. An intervertebral implant forposterior insertion via a transforaminal window comprising: curved,substantially parallel posterior and anterior faces, the posterior andanterior faces extending along a longitudinal axis of the implant; apair of convex narrow ends separating the posterior and anterior faces;superior and inferior faces for contacting upper and lower vertebralendplates, the superior and inferior faces defining a thickness of theimplant; at least one depression in the anterior or posterior face forengagement by an insertion tool; and at least two verticalthrough-channels extending through the implant from the superior face tothe inferior face, each vertical through-channel having a width andwalls on posterior and anterior sides of the width, the walls on theposterior and anterior sides of the width of the verticalthrough-channels having a thickness greater than the width of thevertical through channels;
 29. The implant of claim 28, furthercomprising a chamfer on the superior and inferior faces at one of theconvex narrow ends to facilitate implant insertion.
 30. The implant ofclaim 28, wherein the depression further comprises multiple recesses forengagement with an insertion tool.
 31. The implant of claim 28, whereinthe implant further includes at least one horizontal through-channelextending through the implant from the anterior face to the posteriorface.
 32. The implant of claim 28, wherein the implant further includesat least one lateral through-channel extending from at least one of thecurved ends towards the vertical through channel.
 33. The implant ofclaim 32, wherein the lateral through channel extends from one curvedend completely through the implant to the other curved end.
 34. Theimplant of claim 28, wherein the implant is formed from a radiolucentmaterial.
 35. The implant of claim 34, wherein the implant includes atleast one radiopaque marker.
 36. The implant of claim 28, wherein theimplant is formed from a titanium alloy.
 37. An intervertebral implantsized and configured for implantation between a first and secondvertebra via transforaminal lumbar interbody fusion technique, theimplant comprising: curved posterior and anterior faces, the posteriorand anterior faces extending along a longitudinal axis of the implant; apair of arcuate ends separating the posterior and anterior faces;superior and inferior surfaces for contacting at least a portion of thefirst and second vertebral, the superior and inferior faces defining athickness of the implant; at least one vertical through-channelextending from the superior surface to the inferior surface, the atleast one vertical through-channel defining a first wall between theanterior face and the vertical through-channel and a second wall betweenthe posterior face and the vertical through channel, the first andsecond walls having a wall width, the vertical through channel having achannel width, the wall width being greater than the channel width.